He said: “This is symptomatic of factory farming – it’s the underbelly of battery factory salmon farming. Infectious diseases are rife in the industry and about a fifth of farmed salmon stock is dying.

“The fish in these tanks are not going to shops but they have been swimming alongside ones that are.”

The images were taken at Marine Harvest’s site at Gorsten, near Fort William, and Scottish Salmon Company’s Strondoir Bay site, near Ardrishaig on Loch Fyne.